The present invention relates to a process for preparing spheroidal silica-alumina particles.
The metallic oxides and particularly the mixtures of aluminium oxide and silicium oxide or silica-alumina, are widely used in the chemical industry. For the most of these applications, it is preferable to use the silica-alumina in the form of spheroidal particles or beads. Among the main advantages of these beads are better wear and crushing strength. Also, these beads may be more evenly distributed throughout the reactors in which they are placed thereby reducing the pressure drop through such reactors.
In order to obtain metallic oxide beads of uniform sizes, a hydrosol of the particular oxide generally is introduced as droplets into a hot and practically water-immiscible fluid, acting as a gelitination medium. The application of such a method to produce silica-alumina beads presents some disadvantages. Indeed, even if an alumina hydrosol is used as the alumina source, the gelitination time of the silica-alumina mixture dispersed as droplets is particularly long and does not permit the beads to be produced in a commercially feasible time for industrial applications. To remedy this disadvantage, a gelitination agent must be used, particularly a weak base. Additionally, the beads obtained generally must be immediately subjected to an aging treatment. When compounds other than hydrosols are used as the alumina source, the addition of a gelitizing agent generally gives mixtures which prematurely stiffen and which cannot be dispersed as droplets into the gelitizing medium.
An object of the present invention is to provide a new method for preparing silica-alumina beads.
Another object of the present invention is to provide a method for producing silica-alumina beads from alumina hydrogel.
A further object of the present invention is to provide a method for producing silica-alumina beads by the method of dispersion into a hot fluid, whereby the wet beads obtained are handleable and stable.
A still further object of the present invention is to provide a direct method for producing silica-alumina beads which, after drying and calcining, have a high mechanical strength and which can be used as catalysts or catalyst supports.
Additional objects will become apparent from the following description of the invention herein disclosed.